Lamp-making method



May'zs, '1942.`

C. A. LAISE LAMP-MAKING METHOD original Filed June '7, 1959 Avl E .N R 0T V... B

Patented Mey 2 6,- 1942 1 OFFICE I LAMP-MAKING METHOD Clemens A. Leise,deceased, late or Tenney, N. J., by Fidelity Union Trust Company,executor,

Newark, N. J., assignor to Callite Tungsten Corporation, Union City, N.J., a corporation of Delaware Original application .lune 7, 1939, SerialNo.

277,944. Divided `and this application Decembei' 3, 1940, Serial No.368,308 v 4 claims. (Ci. 17e-13.2)

'I'he present invention relates toa method of forming a tungsteniilament of high efficiency' adaptable for use in an electricincandescent lamp. An important feature .of the invention'resides in thefact that scavenging materials are included in the slug from which thelaxnentv isV drawn, and the lament so formed is then given aheat'treatment in an atmosphere of wet hydrogen whereby the scavengingmaterials are distilled out and all impurities are eliminated.

lThe illament resulting from this treatment conysists of longinterlocking sections and can be operated at high emciency and longlife.

AThis application is a division of copending application Serial No.277,944, led'June 7, 1939, by the executors of the last\will andtestament of Clemens A. Laise, deceased.

The expression "high eiiiciency" as used in the present applicationneeds a certain.denition. It is probably true that this term has been inuse since the early days of'the lamp art. It is certainly true that withthe introduction of metallic laments, the lamps utilizing thesefilaments became known as hi/gh emciency lamps. The term, however, hadmeaning only4 in comparison with carbon lamps and other lamps of lesseremciency. With the appearance of the tungsten l iilament lamp, the termacquired a new meaning and when this was followed by the gas-iilled lampwith a coiled tungsten iilament, -it was thought that a lamp of thistype was the high efliciency lamp.

Developments of recent years, however, have shown still higheremciencies are possible. For, whereas'in former times each increase ineiiiciency was attained by use of an improved 'lilament material or byuse oi' a more suitable gaseous atmosphere, it has lately( been the aimto use the same gaseous atmosphere and the same lament material but toattain greater emciency by applying more exact engineering principlesvto the lamp construction.

JInthe lamp art; efliciency consists in obtaining kthe greatest amountof lumens per watty consistent with a suiciently long life to satisfycommercial and practical needs. As eiiiciency is increased the life ofthe lamp is shortened, other things being equal. vIn the lamp art of thepast, however, the highest possible efciency was rarely attained for thereason that such a lampV was not well adapted to sustain the shock ofturning the current on or oi. A metal lament is most conductive whencold; but as the temperature increases, the resistance also increases.There is, therefore, at the instant o! switching on. a

sudden surge` of current through the filament which produces a shocksuflicient in many cases to rupture the lament.

It is an object of the present invention to pro- Y vide as a product ofsaid method a lamentthat,

when used in a lamp,vis capable of obtaining an extraordinarily highemciency and a long commercial life. In Patent No. 1,631,493 issued toClemens A. Laise. on June '7, 1927, there is described and claimed aprocess of making a refractory metal product consisting of tungstencontaining certain scavenging bodies such as boron nitride. When thismetal was made into a slug it could be drawn down into a very ne grainediilament suitable for an electric incandescent lamp. The iinishedlamentary body might contain as little as 1% and as high as 20% of boronnitride, and as such it formed a vvery suitable and emcient iilament foran electric incandescent lamp of the time that patent was issued. Thelament of the present invention may befconsidered as of the general typede-v scribed and claimed in said Patent No. 1,631,493 in that the slugfrom which it is drawn consists mainly of tungsten but has an additionof boron nitride or boron suboxide and potassium borate, all of whichhave a scavenging eiiect. However, in contradistinction to said patentabove mentioned, the metallic bar or slug from which the iilament ofthis" invention is drawn is so treated in the iinal filament the amountremaining is very minute, being one-fourth of one per cent. or less.

The lament drawn from this slug so prepared is substantially puretungsten, but owing to the-treatment hereinbefore referred to andhereinafter more particularly described, the lament has few sectionalboundaries, if any, in relation to its length. The lament metal `isrelatively soft and pliable and. the sectional boundaries where theyoccur interlock laterally and longitudinally of the wire in such amanner that during burning inl a lamp there is only very slight tendencyto sag, offset or rupture, and, the intergranular cement beingreduced`to a minimum, the filament has little tendency to twist ordistort after it has been shaped and set into suitably concentratedform. One prime cause of brittleness in tungsten laments of the granulartype of the prior art as represented in Patent No. 1,631,493, and inmost filaments of that time, is the presence of foreign non-metallicsubstances in the grain boundaries, and in the fact that the filamentshave a very large number of small grains rather than large crystals suchas are contemplated in the present invention. For instance, in the oidpressed or squirted tungsten'laments, an organic binder was used whichbecame carbonized during the process of manufacture and formed carbidesin the crystal boundaries. In the drawn tungsten filaments as .formerlyproduced, additions of various subsilicon hydrides in the grainboundaries, with l a resulting brittleness after relatively short use.

All such intergranular substances act solelyas cements holding thegrains together and preventing the grains from coalescing and forminglarger grains. Inthe slug from which the lament of the present inventionis drawn, however,

. the cementing material is composed of scavengnitrides may be used withexcellent effect, such as barium nitride and beryllium nitride.

The heat treated coil and mandrel are then cut to proper lengths to givethe proper voltage of lamp and the mandrel is then dissolved in suitableacids such as nitric acid and sulphuric acid if nickel or nickel alloysare used as mandrel wire.

After the coil or other shape of @lament treated in the above manner ismounted into the lamp, the lamp is sealed and exhausted or filled withgas and then flashed by connecting the lamp in series with a rheostato'r nichrome resistance at about 125% over voltage, that is, 125% of therated voltage of the filament for a period of about five minutes, sovthat the filament quickly attains the germinating temperatures and -thegrains coalesce or flow into each other, producing a light-emittingmedium with long inter- .l-.-

locking sections which have little tendency to sas or distort. Suchsections may consist of at least one turn vand preferably several turnsof coil,

especially after the lamp has burned about one hour guts rated voltage.

During the hashing operation it is desirable to use twice the voltage ofthe greatest voltage of the lamp and so regulate the proper voltage Arheostat.

treatment are so regulated that they have a grain count ofapproximatelyf15,000 to 20,000 grains per square millimeter.

- 'Ihe slugs are mechanically worked by swaging and drawing into wire,and then concentrated into coils or coiled coils or rolled into ribbonand corrugated or twisted into concentrated form. In making coiledcoils'of filament wire, the wire should be so wound that the magneticeffect due to the lines of force generated by it will not causeshort-circuiting. When making coils or coiled coils, mandrels of 'nickelor nichrome or other refractory metals soluble in acids may be used, andthe coil or coiled coil lis heated on the andrel in an atmosphere of wethydrogen at 'mperatures ranging from l000 C. to 1500* C. until apermanent set is imparted to the filament and the wire has been relievedof all of its strain. Thus, there will be no readjustment of the coilafter the mandrel is dissolved out.

Wet hydrogen is used, a practice contrary to that of the present art inwhich dry hydrogen is used in such operations. Wet hydrogen tends todecompose any carbides that may be on the surface or in the grainboundaries of the filaments.

If dry hydrogen is used,Y carbides are likely tov form with the filamentmetal in the presence of carbon or carbon compounds. As a result of thisprocess of using wet hydrogen, pliabiiity and ductility of the lament isnot impaired as it would be if dry hydrogen were used.

- In thefdrawing Fig. 1 illustrates a longitudinally sectional view ofthe filament of this invention, and Fig. 2 illustrates a' cross-sectionthereof.

It is apparent that this filament of few interlocking sections can bevoperated at amuch higher emciency or lumen output and longer life thana highly crystallized filament' of many grain boundaries. Furthermore,it retains its shape after it is once permanently set or flashed by myspecial yprocess in the lamp circuit of thisv invention, so that it doesnot droop, shrink.'

containing boron scavengers, or the like, is subjected in my specia'lcircuit to a flashing or heat treating operation after the lamp isexhausted or even after it is'based to produce the final structure in mylight-emitting element as previously set forth.

'I'he filament of this invention is preferably mounted upon lead wiresof the general type described and claimed in the patent to Clemens A.Laise and Jacob Kurtz No. 2,120,561, dated June 14, 1938. Because of theexceptional heat and current conductivity characteristics of thematerial of these lead wires, they maybe made much smaller in 'diameterthan in thecase of lead wires generally used in lamps of the present artAof an equivalent wattage and may be as small as 50% of thecross-sectional area of-the enging materials mentioned, other refractory75 lead wire of .such generally used lamps.

Having'thus describedthe invention,'what is claimed is:

1. The method of forming a concentrated tungsten lament which comprisesdrawing a iiiament from a tungsten slug containing scavenging material.then coiling the fllament into coiled coils, then heating said coiledfilament to 1000 C. to 1500 C. in an atmosphere of Wet hydrogen,thereafter mounting said coiled lament in a lamp and flashing the sameby connecting it in series with a resistance and impressing thereon avoltage of lal'iproxiinately 125% of the rated voltage of the-.lampuntil the scavenging materials are substantially distilled out and thela-f ment materials form into long interlocking grains.

2. The method of forming a concentrated tungsten lament by heating thesame in an atmosphere of wet hydrogen, then mounting the .filament in alamp circuit having a resistance a wire, coilingthe wire, coiling-thecoils, heating said coils in an atmosphere of wet hydrogen, and thenmounting the iilarnent in a lamp circuit having a resistance element inseries with the lament 'and applying thereto a difference of potentialso as to instantaneously bring said filament to its germinatingtemperature, thereby rst causing the distillation and eliminationv ofimpurities from the grain boundaries and then causing the coalescence ofits constituent grains into relatively long interlocking sections.

4. The method of forming a concentrated filament which comprises drawinga filament from a tungsten slug containing scavenging materials,concentrating the lament, heat treating the concentrated iilament'at atemperature of 1000 C.l to 1500 C. in an atmosphere of Wet hydrogen, andthen heating saidfllament by connecting it in series with a resistanceto the germinating temperature in a suitable atmosphere until saidscavenging materials are substantially distilled out and the ilamentforms large interlocking grains.

v FIDELITY UNION TRUST COMPANY,

By LESLIE G. MCDOUALL,

Vice-President Sole Surviving Eecutor of the Last Will-and? Testament ofClemens A. Laise, Deceased.

